Neurosurgery routinely involves performing craniotomies for exposure of the brain and intracranial contents for various intracranial pathologies including tumors, head injuries, vascular malformations, aneurysms, infections, hemorrhages, strokes, and brain swelling. A craniotomy involves creation of burr holes and removal of a portion of the skull (bone flap) with subsequent approximation of the bone flap for closure. Several methods and fixation devices are available for re-attaching the bone flap to the skull including small metallic or absorbable plates with screws or wires. Another method has been the use of cranial clamps consisting of two connected circular elements placed on the inside and outside surfaces of the skull. All of the aforementioned cranial fixation devices in the prior art provide for a rigid fixation of the bone flap to the skull.
In cases of post-operative intracranial hemorrhage and/or brain swelling development, a decompressive craniectomy is performed. Decompressive craniectomy is a neurosurgical procedure used to treat increased intracranial pressure (ICP) from head injury, stroke, brain tumor, infection, cerebral hemorrhage, and space occupying lesions. The technique involves removal of the skull and opening of the dura mater covering the brain, thereby allowing the swollen brain to herniate outwards through the surgical skull defect rather than downwards to compress the brainstem. The procedure improves outcomes by lowering ICP, the pressure within the skull. Increased ICP is very often debilitating or fatal because it causes compression of the brain and restricts cerebral blood flow. The aim of decompressive craniectomy is to reduce this pressure. The larger the removed bone-flap is, the more ICP is reduced. Following removal of the bone flap, the dural opening is closed with a patch graft taken from a cow, pig, cadaver, or a synthetic graft. The preferred method is a synthetic collagen matrix since it is capable of expanding. In addition to reducing ICP, studies have found decompressive craniectomy to improve cerebral perfusion pressure and cerebral blood flow in head injured patients.
Decompressive craniectomy is used to treat major strokes associated with malignant brain swelling and increased ICP. It is well known that a decompressive craniectomy improves survival and functional outcome in patients with severe brain swelling from head injury or stroke if performed in a timely manner. There usually is an inherent time delay between diagnosing the cause of the increased intracranial pressure and performing the decompressive craniectomy. Typically, once a post-operative increase in ICP is detected, either through a clinical exam or an ICP monitoring device, medical treatment is initiated and a CT or MRI imaging is obtained to identify the underlying cause of the raised intracranial pressure. If the need for a re-operation or decompressive craniectomy is identified, the anesthesiologist and operating room staff are notified and the surgery is subsequently undertaken. Unfortunately, at times the operating room and/or staff are at full capacity necessitating further delay until the surgery can be performed. Despite the best of attempts by the surgeon, in cases of massive brain swelling or a rapidly developing post-operative hemorrhage, the patient may end up with irreversible brainstem injury with consequent vegetative state or death.
After a craniectomy, the risk of brain injury is increased because of the removed bone flap, particularly after the patient heals and becomes mobile again. Therefore, special measures must be taken to protect the brain, such as a helmet or a temporary implant in the skull.
When the patient has healed sufficiently, the craniectomy skull defect is usually closed with a cranioplasty. Cranioplasty is repair of a defect in the vault of the skull. This repair can be carried out by using bone removed at earlier surgery that has been preserved or by using bone from elsewhere as a graft. The iliac bone bounding the pelvis, ribs and even a part of adjacent skull bone can be used. If possible, the original bone flap is preserved after the craniectomy in anticipation of the cranioplasty. The bone flap is usually stored sterilely in a freezer until the patient is ready for implantation of the bone flap into the craniectomy skull defect. Typically, this time period can last several months since it may take this long to treat the underlying cause of the increased intracranial pressure. This extended time period not only increases the risk of brain injury but also increases the risk of infection in the stored bone flap. Another technique of storing the removed bone flap involves placing it under the skin in the abdomen. This requires a surgical procedure to place the bone flap in the abdomen and another one to remove it, thereby also increasing the consequent risks to the patient. In cases where the bone flap cannot be replaced due to infection or any other reason, the skull defect is repaired either with a prosthetic plate or a titanium mesh and bone cement. A prosthesis obviously cannot completely replicate the original skull defect and therefore, some cosmetic deformity persists following a prosthetic cranioplasty. The prosthesis also increases the risk of infection.
The risks associated with cranioplasty include infection, hemorrhage, brain injury, seizures, and death along with other risks inherent to any surgery and general anesthesia. It is also usually necessary for the patient to be in hospital for a week or so after a cranioplasty.
U.S. Pat. No. 5,902,304 to Walker et al. describes a telescopic bone plate for use in bone lengthening by distraction osteogenesis. The bone plates are attached to osteomically separated mandible or skull sections connected by a thread screw assembly. The extent of the required distraction can be adjusted by an external screwdriver. U.S. Pat. No. 5,993,448 to Daniel J. Remmler describes a skull fixation device for treatment of craniofacial deformities that provides for relative movement of the skull segments by a percutaneously placed external wrench. U.S. Pat. No. 6,187,004 to Jeffrey A. Fearon describes a mandible or skull expansion plate. The extent of the expansion is adjusted by an externally placed device.
The aforementioned cranial fixation devices in the prior art provide for treatment of craniofacial defects in particular craniosynostosis. They all require an external screwdriver to control the extent of the skull movement allowed and they do not describe or provide for outward or inward movement of the both flap relative to the skull in response to a change in the intracranial pressure.
U.S. patent application No. 60/812,105 to Kathryn Ko describes a method of performing decompressive craniectomy with the bone flap attached to the skull with a hinged plate. The method describes attaching the hinged plate to one end of the bone flap and a rigid plate to the other end. The described method also requires a re-operation to fixate the unconstrained bone flap at the rigid plate end to the skull. U.S. patent application Ser. No. 12/033,815 to Tucci also describes a method similar to the Ko application of attaching the bone flap to the skull with a hinged plate at one end of the bone flap and a straight plate at the other end with unconstrained bone flap movement. They also describe a deformable plate which could be used instead of a hinged plate for bone flap attachment. This construct would also require a re-operation to fixate the unconstrained bone flap at the straight plate end. Tucci also describes a two part sliding device for cranial fixation. The device is not very practical as it very significantly sticks outwards from the skull surface and has a very high profile and obvious painful cosmetic defect with overlying skin irritation and risk of erosion/infection. This device would also require another operation to remove it once the bone flap approximates to the skull.
Considering the aforementioned complexities and risks involved in the post-operative management of critically ill patients undergoing a craniotomy, there is a need for a better technique which provides for cranial fixation along with immediate treatment of increased intracranial pressure and avoids the need for performing a subsequent cranioplasty.